The evolution and formation of a redox front in the near field of a repository for high-level nuclear waste is modeled, considering the effect of a time-dependent source term of the oxidizing species produced by radiolysis of the water entering the canister. The transport of oxidants in the clay surrounding the canister occurs by diffusion. In the rock, the transport of oxidants is modeled as occurring through fractures, with diffusion into the rock matrix. The results show that it is not probable that the redox front will ever move past the bentonite. If it does, the tips of the redox front may move <100 m over a million year period in a channel with a high flow rate.